The gravitational waves from the bubble collision can be obtained with the envelop approximation [1]}, [2]}, [3]} is [4]},
\(\Omega _{\text{col}} h^2 =& 1.67\times 10^{-5} \left(\frac{H_{\ast }}{\beta }\right)^2\left(\frac{\kappa \alpha }{1+\alpha }\right)^2 \left( \frac{100}{g_{\ast }} \right)^{1/3}\nonumber \\&\left( \frac{0.11 v_b^3}{0.42 + v_b^2} \right)\frac{3.8(f/f_{\text{env}})^{2.8}}{1+2.8(f/f_{\text{env}})^{3.8}} \; .\) 
